Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
206208
Case 6053
CEB:am
IMPROVED METHOD FOR PRODUCING FRICTION COMPOSITIONS
Field of the Invention:
This invention relates to the production of friction
brake shoe compositions and more particularly to the
production of railroad brake shoes without the use of any
volatile solvent.
Background of the Invention:
The friction composition for railroad brake shoes usually
contains four functional groups of ingredients, namely bonding
materials, organic and carbon based fillers, inorganic fillers
and reinforcing fibers including synthetic and natural organict
fibers. The bonding materials provide a curable matrix to
hold a uniform dispersion of the fillers and reinforcing
fibers and usually comprise both a vulcanizable natural or
synthetic rubber and a thermosetting resin of natural or
synthetic source. Typically the rubber component has been
butyl rubber, a styrene butadiene copolymer rubber, an
acrylonitrile rubber, a chlorinated butyl rubber, or mixtures
thereof, along with a curing agent such as sulfur or 2-
mercaptobenzothiazole, tetramethylthiuram disulfide and may
also include minor amounts of stiffening agents such as carbon
black, magnesium oxide and zinc oxide. Normally the
thermosetting resin has been a phenol-aldehyde resin or cashew
nut shell oil partially polymerized with an aldehyde, and
mixtures thereof. If the resin component is not self-curing,
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an independent curing agent such as hexamethylene-tetramine is
included in the bonding matrix.
Suitable organic and carbon based fillers have included
petroleum coke, coal, graphite (both natural and synthetic),
neoprene scrap and fully cured cashew nut resin. The purpose
of such organic and carbon based fillers is to provide bulk to
the final composition and to control friction at elevated
operating (braking) temperatures.
Inorganic fillers function to largely supply the
frictional coefficient of the final composition and to absorb
frictional heat during braking and typically have included
iron grit, iron powder, red iron oxide, sand, aluminum silicate°
(kyanite), barytes, rottenstone, clay, aluminum trihydrate,
magnesium oxide and zinc oxide.
The reinforcing fibers serve to provide tensile strength
and shear resistance in the final composition. Historically,
asbestos was favored as a natural reinforcing fiber. Other
natural fiber sources are wollastonite (calcium silicate) and
mica. Manufactured fibers include glass fibers, steel wool,
alumna-silica ceramic fibers and most recently favored aramid
polymer fiber and acrylic fibers.
Examples of prior railroad brake shoe production and the
ingredients and methods therefore are disclosed in U.S.
patents Nos. 4,169,680, 4,219,452, 4,313,869 and 4,466,513.
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Heretofore it has been necessary to dilute the bonding
materials with a volatile solvent such as toluene so as to
provide sufficient fluidity to enable the additional
ingredients to be wetted and dispersed therein and to permit
introduction of fragile reinforcing fibers without destroying
or damaging the structure thereof. Subsequently, the solvent
was driven out of the composition by vacuum heating. The need
for such a solvent has been a disadvantage for a number of
reasons including the cost of the solvent and equipment to
recover and recycle same. Moreover, it has been nearly
impossible to prevent loss of some solvent with attendant
environmental and employee health concerns.
Summary of the Present Invention
The present invention provides a method for mixing the
ingredients of a railroad brake shoe composition without
employing a volatile solvent. The present invention provides a
method for mixing the ingredients of a railroad brake shoe
composition without damage to friable reinforcing fibers but
in the absence of evaporable diluent. The present invention
provides a method for mixing the ingredients of a railroad
brake shoe composition wherein the bonding ingredients are
made sufficiently fluid for the dispersion of filler and
reinforcing ingredients without the use of a diluent solvent.
The present invention provides an improved method for
producing a railroad brake shoe.
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In general, the present invention involves the fluidizing
of a friction material bonding matrix by combining a blend of
highly polymerized cashew nut shell liquid resin and a minor
amount of a reactive diluent, such as acid treated raw cashew
nut oil, furfural alcohol resin or liquid phenolic resin, with
a quantity of an uncured rubber compound, and mechanically
shearing (mixing) the bonding matrix in the presence of high
surface area inorganic fillers. Upon the mixture reaching the
consistency of a paste that is sufficiently fluid to permit
introduction of friable material without damage all of the
additional ingredients, i.e. organic and inorganic fillers and
reinforcing fibers, in the absence of any diluent solvent, are
added and mixing continued without degrading their required
morphology and until the latter are uniformly dispersed in the
bonding matrix. Thereafter the resulting composition is
shaped, cured and adhered to a brake shoe backing plate.
In one aspect, the invention provides a method for
manufacturing a friction composition material for railroad
brake shoes, the composition material having a bonding matrix
of bonding materials with fillers and reinforcing fibers
dispersed uniformly therein, the method comprising: providing
at least one inorganic filler with first surface areas, a
first quantity of a blend of a non-volatile reactive diluent
and an uncured highly polymerized cashew nut oil resin, which
reactive diluent is between about 10% to 30o by weight of the
first quantity, a functional amount of a resin curing agent
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and, a second and lesser quantity of styrene butadiene rubber
crumbs along with a functional amount of a vulcanizing agent
for the rubber; mixing initially the first and second
quantities in the presence of the at least one first surface
area filler ingredient to form a fluid paste with a
consistency to accept dispersion of the fillers and fibers
without damage to the structures thereof; providing at least
one filler with second surface areas less than the one
inorganic filler first surface areas; then adding the at least
one second surface area filler and reinforcing fibers to the
fluid paste; continuing the mixing of the fluid paste, fillers
and reinforcing fibers to form a uniform dispersion, the
reactive diluent operable to provide sufficient fluidity to
the fluid paste for wetting of the fibers and fillers.
In a further aspect, the invention provides a method for
manufacturing a friction brake shoe composition pre-form of a
bonding matrix free of volatile solvent additions and having
friction fillers and reinforcing fibers uniformly dispersed in
the matrix, the method comprising: providing at least one
inorganic filler with first surface areas selected from the
group consisting of clay, red iron oxide and carbon black;
providing as bonding matrix materials in the absence of the
volatile solvent additions, a first quantity of a blend of an
uncured highly polymerized cashew nut oil resin, an acid-
treated raw cashew nut oil, a functional amount of a resin
curing agent, a second and lesser quantity of styrene
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butadiene rubber crumbs and, a functional amount of a
vulcanizing agent for the rubber; mixing the first quantity
and the second quantity in the presence of the at least one
first surface area filler to form a fluid paste; providing at
least one filler with second surface areas less than the first
surface areas, the second surface area filler selected from
the group consisting of aluminum silicate, coke fines and
graphite, and providing reinforcing fibers selected from the
group consisting of glass fibers and aramid fibers; adding the
second surface area filler and the reinforcing fibers to the
fluid paste; continuing the mixing of the fluid paste, first
and second area fillers, and the reinforcing fibers to form a
uniform dispersion, the acid-treated raw cashew nut oil
operable as a reactive diluent to provide sufficient fluidity
to the fluid paste for wetting the fibers and fillers; and
compressing and shaping a portion of the uniform dispersion to
form a briquette-like pre-form of a friction composition.
In a still further aspect, the invention provides a
method for manufacturing railroad brake shoes of a composition
material, which has bonding materials with fillers and
reinforcing fibers, and is prepared in the absence of a
volatile solvent addition to the composition shoe material,
the method comprising: providing at least one inorganic
filler with first surface areas, a first quantity of a bonding
matrix material of an uncured highly polymerized cashew nut
oil resin, an acid-treated raw cashew nut oil, a functional
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amount of a resin curing agent, a second and less quantity of
styrene butadiene crumbs along with a functional amount of a
vulcanizing agent for the rubber; mixing initially the first
and second quantities in the presence of the at least one
first surface area filler ingredient to form a fluid paste
with a consistency to accept dispersion of the fillers and
fibers without damage to the structures thereof; providing at
least one filler with second surface areas less than the one
inorganic filler first surface areas; then adding the at least
one second surface area filler and reinforcing fibers to the
fluid paste; continuing mixing of the fluid paste, fillers and
reinforcing fibers to produce a uniform dispersion, the acid-
treated raw cashew nut oil operable to provide sufficient
fluidity to the fluid paste for wetting of the fibers and
fillers; providing a brake shoe backing plate; shaping the
uniform dispersion material to the brake shoe backing plate;
and, applying heat and pressure to the uniform dispersion
composition material to effect curing of the bonding matrix
material and to adhere the composition material to the brake
shoe backing plate.
Detailed Description of the Invention and a Preferred
Embodiment:
In the preparation of a suitable friction composition, a
bonding matrix of rubber and resin is first produced in a high
shear mechanical mixer such as a sigma blade type double-arm
mixer such as is available from Baker-Perkins Inc. of New
York, N.Y. Selected quantities of both subdivided
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unvulcanized rubber, preferably crumbled, and a special blend
of uncured highly polymerized cashew nut oil resin with 10-
30~, by blend weight, of a reactive diluent such as acid
treated raw cashew nut oil, furfural alcohol resin or liquid
phenolic resin are placed in the mixer along with minor
functionally sufficient quantities of rubber vulcanizing and
resin curing agents, preferably sulfur and hexamethylene-
tetramine, respectively. Added to the foregoing ingredients
are quantities of inorganic fillers having relatively high
surface to weight ratios, such fillers and quantities being
selected to give desired known properties to the final
friction composition. In the preferred bonding matrix, these t
fillers may include powdered clay, baryte, alumina trihydrate,
rottenstone, magnesium oxide and red iron oxide dust. Carbon
black may also be included. These high surface area fillers
are found to have absorptive and abrasive qualities that
enhance the shearing action of the mixer and thereby promote
the rapid production of a uniform rubber-resin fluid paste
within about two (2) to ten (10) and preferably about four (4)
minutes of high shear mixing time. The point at which the
paste-like, but sufficiently fluid to accept friable material,
consistency is achieved is more precisely indicated by the
time following start-up at which the electric current
(amperage) drawn by the mixer motor begins to decline after
first peaking.
5
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Thereafter, the remaining friction composition
ingredients comprising all remaining fillers, reinforcing
fibers, vulcanizing and curing agents are added to the bonding
paste and mixing is continued without damaging fiber
morphology for about an additional twenty (20) minutes or
until a uniform dispersion of fillers and fibers throughout
the bonding media is achieved. As heretofore indicated, the
vulcanizing and curing agents are usually introduced into the
composition along with the rubber and resin ingredients and
stiffening agents.
After the mixing is completed, the friction composition
is further processed in a manner similar to prior procedures
for producing friction shoes and the like. Normally this will
entail shaping and pressing quantities of the friction
composition into pre-forms of required shape and then molding
and heating the shaped composition, under pressure, to cure
and harden the rubber-resin matrix. These procedures may
include pre-reduction of the friction composition in a hammer
mill, or the like, to produce uniform size particles to
facilitate handling and the charging of measured quantities of
the composition into pre-form cavities.
For the production of railroad friction shoes, where the
friction composition is bonded to an arcuate steel backing
member, the friction composition will typically be pre-formed
into a briquette having an arcuate shape and the requisite
weight desired for the brake shoe; and the briquette is
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2062084
subsequently assembled with a steel backing plate within a
mold-press where it held at about 2500 psi and about 350°F for
a period of about twenty minutes (20) which is sufficient to
vulcanize and cure the rubber-resin matrix and bond same to
the backing plate.
Examples 1-10
The following tabulation of examples show a variety of
railroad friction brake compositions with ingredients by
weight percentage of each entire composition. Among these raw
cashew nutshell oil is a preferred reactive diluent and
Example 3 represents a preferred composition. Each
composition of the examples is prepared in accordance with thet
aforedescribed procedure. It is to be noted that in each
example the blend of polymerized liquid cashew resin and
reactive diluent (either raw cashew nutshell oil, furfural
alcohol resin or liquid phenolic resin) includes an amount of
reactive diluent that is about 10% to 30% of the two combined
ingredients.
7
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206084
Another friction composition for railroad brake shoes
comprises the following ingredients:
Ingredient speci fic Gravity Weiq~t Volume
%
Bonding Materials
Blend of Polymerized Cashew
Nut Oil Resin with 20%
Acid Treated Raw Cashew
Nut Oil 1.03 16.77 30.44
Styrene Butadiene Rubber
Crumbs 1.00 7.74 14.47
Sulfur 2.07 1.66 1.50
Hexamethylene Tetramine 1.30 .84 1.21
Zinc Oxide 5.60 .37 .12
Clay 2.45 18.79 14.34
Red Iron Oxide 5.18 15.52 5.60
Carbon Hlack 1.75 3.55 3.79
s
l Fill
i
di
er
:
ona
t
Ad
Kyanite
(3AL203-S102) 3.00 12.95 8.07
Petroleum Coke Fines 1.93 13.62 13.19
Graphite 2.30 4.43 3.60
' Fibers:
forcin
i
R
g
e
n
Chopped Fiberglass
(rubber impregnated) 2.20 2.72 2.31
KEVLAR~ (aramid fiber)
Pulp 1.44 1.05 1.36
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206084
The foregoing detailed description has been given for
clearness of understanding and to provide a complete
description of a preferred embodiment of the invention.
Various modifications may be made without departing from the
spirit and scope of the invention which is defined in the
following claims.
t
